KAUFMAN, Thomas C.; LIU, Paul Z.; Indiana University; Indiana University: The Role of Gap and Pair Rule Genes in the Segmentation of the Germband of Oncopeltus

Segmentation in long germband insects occurs simultaneously across the entire body. A cascade of genes patterns the embryo along its anterior-posterior axis by subdivision of the blastoderm. This is in contrast to short and intermediate forms of segmentation where the anterior segments are formed at the blastoderm while the remaining segments arise at later stages from a posterior growth zone. The biphasic character of segment generation in short and intermediate germ insects implies that different formative mechanisms may be operating in blastoderm-derived and germband-derived segments. In Drosophila, the gap genes hunchback and Kr�ppel are required for proper formation of the anterior and central portions of the embryo respectively. While the pair rule gene even skipped acts downstream of these gap genes and is required for pair-wise segment formation through the length of the germ band. Although we know much about Drosophila segmentation, we still know less about how the blastoderm of short and intermediate germband insects is allocated into only the anterior segments, and how the remaining posterior segments are produced. In order to gain insight into this type of embryogenesis, we have investigated the expression and function of the homologs of the aforementioned Drosophila genes in an intermediate germ insect, the milkweed bug, Oncopeltus fasciatus. We have determined the expression of these genes by in situ hybridization and in order to resolve their role in embryogenesis, we have developed a method of parental RNAi in the milkweed bug. We have found both similarities and striking differences in the pattern of expression and apparent role in segmentation for all three genes in Oncopeltus as compared to other insects including Drosophila and Tribolium.